PROJECT SUMMARY Fatty liver disease (FLD) is a major public health issue affecting millions of people worldwide. Chronic FLD is defined by excess liver fat (hepatic steatosis) and can lead to a more profound disease state of steatohepatitis (SH) that may be reflected in hepatic fibrosis (including severe cirrhosis at the extreme). SH can lead to liver failure or hepatocellular carcinoma (HCC). Multiple risk factors predispose individuals to the development of FLD including biological factors (obesity, insulin resistance, type 2 diabetes) demographic characteristics (e.g. sex, age and ethnicity), behavioral and lifestyle-related variables (e.g., alcohol intake, dietary behavior and physical activity), and both endogenous (e.g., infectious agents such as hepatitis viruses, microbiome variability) and exogenous environmental factors (e.g., exposure to pollutants/contaminants/toxins). Mexican Americans are disparately impacted by nonalcoholic FLD with some of the highest observed prevalences in the world and exhibit a prevalence of cirrhosis that is 9 times the national average. Although there is a heritable component of FLD risk, the dramatic increase FLD and HCC prevalence over the past 20 years clearly points to a major role for environmental factors since genetic variation is effectively constant on such a timescale. In this project, we will use high-dimensional omic characterization of Mexican Americans living in South Texas to assess the FLD-relevant environmentally determined exposome. We will recruit 1,000 participants from the longitudinal San Antonio Mexican American Family Study (SAMAFS) to undergo magnetic resonance imaging (MRI) to obtain measures of liver fat and liver fibrosis. Each participant has previously been completely genetically characterized by whole genome sequencing, and the WGS data will be employed to optimally identify the exposome for FLD risk in a minority population. To achieve these objectives, we will: (I) perform MRI-based measures of liver fat/fibrosis and omic characterization of 1,0000 individuals from large extended SAMAFS pedigrees, including metabolomic profiling, lipidomic profiling, epigenomic analysis, and transcriptomic sequencing; (II) detect environmental effects on FLD risk using a novel statistical genetic approach to maximize systematic environmental signals and search for environmental factors reflected in high-dimensional metabolomic/lipidomic, epigenomic, and transcriptomic biomarkers that are correlated with FLD risk; (III) characterize/classify environmental signals with regard to major environmental domains through the identification of non-random spatial distribution, or correlation with known components such as dietary behavior, socioeconomic factors, exogenous exposures, etc.; (IV) detect genotype x environment interactions using the omic data to detect genetic factors involved in the differential response of FLD risk to novel environmental factors. Overall, the ability to identify novel environmental determinants of chronic liver disease risk in an ethnic minority population provides a major opportunity to speed the development of improved targeted treatments.